Engine miss is killing me!

[Steverino]

This is a long story.....I drove my car (06 Aveo Sedan) home one night and ran great. I usually park it in the garage but decided to park outside as I had to return to work early the next day. The car had a slight miss. After work I let my wife drive it home and she said it had a bad miss and check engine light on. I pulled the top engine cover and found that a mouse had eatten through and removed about an inch of #1 plug wire and made a small nest on top of the valve cover. I replaced the wires and checked the plugs. I started it and had a miss yet. I figured the coil pack took a hit from running it with the open plug wire. I replaced the coil pack with a used one due to long wait times for a new one. It had the same miss. I installed my original plugs that I saved as spares and the miss was still there. I could now hear a vacuum leak. I removed the EGR valve and ran with me holding a rag hard against where it would be, miss still there. I used an electronic "ear" to find it at the intake manifold at cylinder #4.I changed the intake gasket (fun!). The car ran better but still had a miss. The old gaskets by the way were chewed on! That is right, all 4 had teeth marks where something ate the little tits to hold them in place and the gasket #4 was broken. I had a local shop scan it and they suggested replacing the fuel injectors. After some trouble I found out I have 2007 style injectors in my 06 and had to get them from the dealer. The shop noted the miss fires were coming from cylinders #3&4. They did a compression test on just number 4 and was about 125 lbs. I replaced just those 2 injectors and still has the miss. I have a scanner and the miss is still on 3&4. If you get the engine rpm's over 1500 the miss goes away and the scanner also verifies it. It does have a fair amount of water coming out of the tailpipe, yes water not coolant. I am running out of ideas here. I do not know how that much stuff can happen over night. I do not see any signs of other chewing on wires or lines. I am going to do a full compression test, check fuel pressure, double check firing order. The timing belt was changed at 60K and now has 80K on it. I was even guessing top O2 sensor but should not cause a miss fire in 2 cylinders. I am also thinking about checking the timing belt marks. Running out of ideas here.

[avguy]

What was the CEL code - random misfire probably? How did the plugs look - did #4 look much different from the others? Did they have the characteristics of an engine in good condition? Just a couple of things you didn't mention, that I'll ask about (which you've probably already eliminated). The rest of the mouse family living in the air filter/box? And since these critters are good enough to occupy the valve cover, maybe they're even broken through the plastic in the air filter and are moving into the TB. Speaking of which, has that been cleaned of carbon deposits recently? And there's always the TPS as a possibility. Probably none of those things though. If you're still stuck with nowhere else to go how about a vacume test, block test for combustion gas, and a leak-down test? Good luck with it!

[Steverino]

It did have a random misfire code. The plugs looked great and #4 looked no different. I did check the air box and it was clean, the hose from it to the TB had tears in it and a friend gave me a good used one from a 2009 Aveo which is just a bit different but works. I cleaned the TB very well when I changed the intake manifold gaskets and did an in the car cleaning about a year ago also. I use an actual TB cleaner spray and an old tooth brush. I looked at the intake valves through the head when the intake manifold was off and they looked very clean. I was going to put the vacuum gauge on it and do a leak-down test. I am not sure what a block test for combustion gas is?

[avguy]

The block test basically is a check to see if a head gasket is leaking and pushing combustion gas into the cooling system. A tester containing special fluid in it is attached to the cooling system, and then the fluid changes color if combustion gas is circulating within the system. It's a fairly common situation with gen 7 Honda Civics. I don't think these testers are available to rent, so it's probably a shop-only thing. And I don't know if a bad head gasket can cause a similar thing in our Aveos, so it's probably a last-resort test.
One question on your problem description. You said there was a slight miss - did you mean just starting on the morning of the problem day, or had the slight miss been happening for a while? The vacuum and compression/leak-downs hopefully get you going in the right direction on this. But if nothing shows up there, you might want to consider the IAC and TPS. Neither of those is likely to cause a sudden miss, but then again sometimes sensors like these do weird things when they begin to head south.

[Steverino]

I do have this tool but never heard the test called that. The miss started right after the mouse damage to the spark plug wire. I did try something....I removed the upper O2 sensor and ran the car and the miss was gone. I put the sensor back in and left it unplugged and ran it and still ran fine. I put a new O2 sensor in and same old problem. When the O2 sensor is unplugged it stays in open loop which tells me it is not a mechanical problem. I took the car to my cousin's auto shop and he got weird readings on his scanner and said the car should be taken to the dealer to have the ECM flashed and relearned. I was thinking the same thing. Compression and fuel pressure tests were all good. I will let you guys know what happens after the dealer looks at it. It may be time to trade in if they can't figure it out.

[avguy]

Did you try the "book" Idle Learn Procedure? I've never actually needed to use it myself, but know the ECM had to do a relearn after a plug issue that mine had a couple years ago. Also, might be tough to get good value on a sale/trade with a miss going on?

[Steverino]

Yes the trade-in value would take a hit but sometimes you have to know when to cut your losses and I'm not saying I would do this unless it was a major item and come near the value of the car. The dealer reflashed, relearned, and updated the ECM and it still ran bad. They did some testing also and happened to check the timing belt and found the dead mouse in the timing belt housing with fur in the teeth of the belt and one cam was 2 teeth off. It seems the mouse got caught in the belt and went through the tensioner and caused just enough slack to have the one cam jump 2 teeth. The belt was corrected and runs great again. I just do not understand how unplugging the O2 sensor whould then get rid of the miss. A friend of mine suggested turning in the damage to my insurance and they are going to cover it after my $100 deductible. Way to go State Farm! Just good to know the dang mouse got his though!

[avguy]

That is one amazing story there Steverino . One day Mickey Mouse squeezes past the top cover, and then brings Minnie and the kids to live in their new home on the top of the valve cover. Then one night one of them goes on a road trip and finds the treadmill in the exercise room. Can't figure out how to get it going, and then you come out in the morning and fire it up. The little guy tries to find the speed control for the treadmill, but gets yanked into a game of bumper pool with the pullys . To come out of that without any serious engine problems is just unbelievably fortunate. And BTW, it would be a federal offense to transport those mice outside of your own property

[Steverino]

LOL....That is pretty funny. I had to show this one to my wife and she laughed also. We should try to get Pixar to do a movie called "Adventure in Aveo Land" that covers that story and the kids can cry when the treadmill scene ends with the family member getting steamrolled. I must say that I do have the dumb luck and wierd stuff following me.